In internal combustion engines, an engine crankshaft is the primary source of torsional load. A crank gear is typically mounted on one end of the crankshaft for driving the engine gear train which includes the cam gear and camshaft among other gear driven elements. Throughout operation of the engine, the torque applied to the crankshaft varies due to, for example, the periodic firing of the engine's cylinders, the engagement and disengagement of driven elements such as a transmission, and the starting, stopping and variations in the speed of rotation of the crankshaft. These torque variations create torsional vibrations which may be transferred to the gear train of the engine often undesirably causing increased noise, premature engine wear and thus reduced gear life and possibly engine failure. In addition, since the engine drive gear train is used to drive engine components which are critical to proper engine operation, torsional vibrations transmitted through the gear train may adversely affect engine operation, such as the accuracy of fuel injection timing.
Many torsional variation absorbing or damping devices have been developed and used in different locations throughout an engine. It is well known to use a damper connected to one end of the crankshaft so as to rotate with the shaft for damping torsional vibrations generated by the crankshaft. Many of these dampers are tuned to approximately the first torsional natural frequency of the crankshaft to provide optimum damping at the natural frequency. Untuned dampers, such as viscous dampers, have an effect at all frequencies, but they provide the greatest reduction in crank torsional vibrations at the crank natural frequency. When the engine operating conditions, i.e. firing frequency or a harmonic of firing frequency, coincides with the natural frequency of the crankshaft, a resonance effect may be created which increases the amplitude of the torsional vibrations thus increasing the likelihood of damage to the crankshaft and other engine components and gears driven by the crankshaft. For example, U.S. Pat. Nos. 1,913,803; 2,926,546; 4,172,510 and 5,188,002; French Patent No. 1,049,924; German Ref. No. 2115099; and U.K. Patent Application No. 2173879 all disclose various types of torsional vibration dampers mounted on a shaft including tuned rubber dampers and viscous type dampers.
Another manner of reducing torsional vibrations in an engine drive train is to use a coupling between a cam gear and the camshaft. For example, U.S. Pat. No. 5,017,178 discloses a resilient coupling apparatus for connecting a ring gear to a camshaft. The coupling includes sets of spring-biased pistons spaced circumferentially around a plate member and mounted in respective bores. Lubrication fluid in the respective bores becomes trapped upon movement of the pistons to viscously dampen the pistons and thus dampen the varying loads transferred to the camshaft from the ring gear or vice versa. However, the use of springs, pistons and a lubrication circuit integrated into a gear connection creates an excessively complex and costly device. Moreover, this device only provides a resilient connection between a camshaft and a ring gear which is driven by a timing gear mounted on a crankshaft and thus only dampens vibrations between these gears. As a result, torsional vibrations generated by the crankshaft will be transmitted to the timing gear and any other gears driven by the crankshaft and the timing gear, causing adverse effects such as increased noise and reduced gear life.
Various torque transmitting couplings capable of damping vibrations have been developed. For instance, U.K. Patent Publication No. 2153489 discloses a torsion absorber device for a friction clutch of a motor vehicle transmission which includes coil spring resilient devices for permitting relative movement between two parallel coaxially mounted disks. The absorber also includes an elastic member or rubber block positioned in an axial groove formed by complementary recesses in the outer surface of a hub and the inner surface of one of the disks mounted on the hub. The rubber block is designed to absorb vibrations transmitted through the connection. However, during compression, one half of the rubber block is subjected to a force in a first direction while an opposing force acts solely on the other half of the block. Therefore, this block is subject to high levels of shear force resulting in rapid block wear and possible failure over time. Also, the hub teeth contact the disk directly to provide an unabsorbed connection between the hub and the disk and therefore this elastic block connection does not provide a dampening connection during all engine operating conditions. In addition, this coupling does not resiliently couple a crank gear to an engine crankshaft and therefore does not prevent crankshaft induced torsional vibrations from reaching an engine drive train.
Russian Patent Publication No. 591637 discloses a shock-absorbing torque transmission coupling for connecting two shafts positioned end-to-end which includes a central shaft having radial vanes extending into respective recesses formed in an outer coupling surrounding the central shaft. Resilient elements in the form of bellows filled with a rubber-like substance are positioned on both sides of each vane between the vane and the recess wall. The bellows function to damp torque vibrations between the connected shafts. U.S. Pat. Nos. 2,012,012 and 2,446,942 disclose similar devices using rubber elements positioned between engaging portions of two couplings to eliminate torsional vibration in the shafts. However, the dampeners disclosed in these references do not resiliently couple a crank gear to an engine crankshaft and therefore does not prevent crankshaft induced torsional vibrations from reaching an engine drive train.
German Patent Publication Nos. 837,343 and 536,684 each appear to disclose torsional vibration dampers or resilient couplings for connecting two coaxial shafts wherein extensions formed on one shaft engage unsupported resilient webs attached to the other shaft. However, these devices rely on the unsupported portion of the resilient elements to transmit the rotative force to the other shaft thus placing a large bending forces on the elements in high load conditions. As a result, the resilient elements are likely to be prone to excessive wear and possibly failure rendering the coupling inoperable. Moreover, this design relies on the connection of the resilient elements to one of the shafts resulting in increased assembly costs and possible disengagement and thus failure of the coupling. In addition, these couplings do not resiliently couple a crank gear to an engine crankshaft and thus do not function to minimize the torsional vibrations in crank gear and associated drive train.
U.S. Pat. No. 4,834,041 to Valev discloses a resilient coupling connecting an auxiliary drive shaft to one end of a crankshaft. The auxiliary drive shaft is used to drive various auxiliary devices such as a generator, a water pump or a fan. Valev also appears to disclose the use of a torsional damper mounted on the end of the crankshaft. However, the auxiliary drive does not drive engine components critical to engine operation, such as fuel injectors and therefore, the resilient coupling does not function to minimize torsional vibrations to ensure proper engine operation, such as fuel injection timing. In addition, this coupling does not resiliently couple a gear to an engine crankshaft and thus does not reduce gear noise and extend gear life.
The technical article PA6-280 by Pielstick appears to disclose a main pinion, i.e. crank gear, resiliently connected to, and driven by, an engine crankshaft via a tuned elastomer type vibration damper. The main pinion is driven directly off the damper inertia ring. The damper appears to include semi-cylindrical resilient members positioned between inner and outer shaft rings located at one end of the crankshaft. The damper functions both as a torsional vibration damping device and an isolator or absorber for minimizing the vibrations transmitted to the main pinion. However, by integrating the damping and isolating functions into a single structure, this damper is incapable of adequately functioning as an isolator for protecting the main pinion and downstream gear train from torsional vibrations at all engine operating conditions. This rubber or elastomer type damper must be tuned to approximately the natural frequency of the crankshaft to permit the damper to dampen the relatively large torsional vibrations caused by resonance when the engine operates at or near the natural frequency. However, when the engine operates below the natural frequency, the damper will not sufficiently function to dampen vibrations but will undesirably transmit torsional vibrations to the main pinion and the timing gear train. Moreover, when the engine operates at approximately the natural frequency, the motion of the damper inertia ring should actually amplify the crankshaft torsional vibrations. The torsional activity of the damper inertia ring is directly applied to the crank gear, adversely affecting engine operation, increasing gear wear and gear noise, and possibly causing gear or shaft failure.
U.S. Pat. No. 1,649,426 discloses a means for preventing the vibrations of the crankshaft from being imparted to a timing chain via a timing gear mounted on the crankshaft which includes an intermediate resilient torque transmitting material, i.e. rubber, positioned in the connection of timing gear to the crankshaft. The rubber material completely fills the space provided between lugs extending outwardly from the crankshaft and inwardly extending lugs formed on the timing gear. This design also uses a friction plate to dampen vibrations experienced by the timing gear by frictionally engaging the timing gear thus assisting in maintaining the proper timing and functioning of parts driven from the timing gear. However, the rubber material completely fills the space between the timing gear and the crankshaft thus restricting the deformation of the rubber material. As a result, use of rubber material having sufficiently high resiliency characteristics necessary for providing sufficient torsional vibration absorption would undesirably permit excessive relative movement between the crankshaft and timing gear resulting in unacceptable timing error while reducing the durable life of the material. On the other hand, use of a resilient material of sufficient stiffness to maintain timing error within acceptable limits would be incapable of adequately absorbing torsional vibrations.
Consequently, there is a need for a simple yet effective crankshaft gear torsional vibration isolator assembly capable of effectively minimizing the transmission of torsional vibrations to the engine's timing gear train throughout all engine operating conditions while maintaining the functional timing relationship between the crankshaft and camshaft.